数据库操作(c#)

windows窗体程序中的数据库操作部分

//数据库连接串
internal static string connstring = "Data Source = 192.168.1.1; Initial Catalog = testdb; User ID = test; pwd = 111111;";        

//学生登录
using (SqlConnection conn = new SqlConnection(login_mainform.connstring))
                {
                    string sql = "select * from test_student where name=@name and pwd=@pwd";
                    SqlCommand cmd = new SqlCommand(sql, conn);
                    cmd.Parameters.Add(new SqlParameter("@name", txtusername.Text));
                    cmd.Parameters.Add(new SqlParameter("@pwd", txtpassword.Text));
                    conn.Open();
                    SqlDataReader reader = cmd.ExecuteReader();
                    Student stu = new Student();

                    if (reader.Read())
                    {
                        stu.Sno = reader[].ToString();
                        stu.Name = reader[].ToString();
                        stu.Major = reader[].ToString();
                        stu.Birthday = reader[].ToString();
                        stu.Sex = (reader[].ToString())==""?"男":"女";

                        Information info = new Information(stu); //新窗口对象
                        info.Show(); //显示学生信息

                        this.Hide(); //隐藏当前窗口
                    }
                    else
                    {
                        MessageBox.Show("输入有误");
                    }
                    #endregion
                }

//修改数据
                using (SqlConnection conn = new SqlConnection(login_mainform.connstring))
                {
                    string sql = "update test_student set pwd=@pwd where sno=@sno";
                    SqlCommand cmd = new SqlCommand(sql,conn);
                    cmd.Parameters.Add(new SqlParameter("@pwd", txtnewpwd.Text));
                    cmd.Parameters.Add(new SqlParameter("@sno", txtsno.Text));
                    conn.Open();
                    int rows= cmd.ExecuteNonQuery();

                    if (rows>)
                    {
                        MessageBox.Show("密码修改成功,请重新登录");
                        login_mainform form = new login_mainform(); //登录窗口
                        form.Show();
                        this.Close();
                    }
                    else MessageBox.Show("存储出错");
                }

//连接数据库查询符合查询条件的数据 adapter
            using (SqlConnection conn = new SqlConnection(login_mainform.connstring))
            {
                conn.Open();
                String sql =String.Format("select sno,name,sex,birthday,major from test_student where name like '%{0}%' and major like '%{1}%' and sno like '%{2}%'", txtnamequery.Text,cmbmajor.Text,txtsnoquery.Text);
                SqlDataAdapter da = new SqlDataAdapter(sql,conn);
                DataSet ds = new DataSet();
                da.Fill(ds);
                }
                

//更新密码
         using (SqlConnection conn = new SqlConnection(login_mainform.connstring))
                {
                    conn.Open();
                    string sno = dgvstudent.CurrentRow.Cells[].Value.ToString();

                    String sql = String.Format("update test_student set pwd = '123456' where sno = {0}", sno);
                    SqlCommand cmd = new SqlCommand(sql, conn);
                    int rows = cmd.ExecuteNonQuery();
                    if (rows > )
                        MessageBox.Show("重置成功。密码：123456");
                    else return;
                }